The present invention is directed to a preheating assembly for heating water using waste heat from a furnace or other heat source. The invention is also directed to a heat exchange assembly for preheating water where the heat exchanger is connected to a flue pipe of a furnace or heating unit.
It is well known that exhaust gases exiting a furnace or heating device from the combustion of a fuel such as oil, gas, coal or wood are at relatively high temperatures. The exhaust gases are typically discharged to the outside such that a large percentage of the heat is not recovered and eventually discharged to the outside.
Many efforts have been made to increase the efficiency of the heating unit by improving combustion and improving the heat recovery of the system. A number of these prior devices are used to preheat water for domestic use by using the exhaust gases from the heating system. One example is disclosed in U.S. Pat. No. 4,406,402 to Henriques. This device discloses a flue gas heat recovery system that includes an air heat exchanger for recovering heat from the exhaust gas. The heated air is then supplied to a second heat exchanger for preheating water which is eventually supplied to a conventional water tank. A control system provides a failsafe system to prevent overheating of the water and the potential danger of overheating the water tank.
A number of devices for extracting heat from waste gases include a heat exchanger that is positioned in the flue pipe or chimney to directly contact the exhaust gases. One example is disclosed in U.S. Pat. No. 4,484,564 to Erickson. This device includes a pipe that is formed into a coil and positioned directly in a chimney. A series of baffles are coupled to the coil to improve the heat exchange between the exhaust gas and the water passing through the coil.
Another example is disclosed in U.S. Pat. No. 4,821,682 to Waters. The device includes an auxiliary storage tank that receives incoming cold water. Water from the storage tank circulates through a conduit loop which extends in a spiral pattern through the flue and through a heat exchanger which concentrates heat generated by the pilot burner. The water that is preheated in the loop is returned to the storage tank for storage until required by the main tank.
Still another example is disclosed in U.S. Pat. No. 4,037,567 to Torres. This patent discloses a heating system including a boiler having an exhaust flue. A pair of concentrically arranged coils are positioned in the exhaust flue and is connected to the conduit for feeding water to the boiler. The water circulates through the loop by natural convection to preheat the water before being supplied to the boiler.
U.S. Pat. No. 4,122,801 to Burns discloses a flue pipe for connecting to a furnace where the flue pipe includes a plurality of spiral coils. The spiral coils are connected to a header pipe for circulating water through the coils to extract heat from the exhaust gas. Still another example is disclosed in U.S. Pat. No. 4,938,172 to Belovarac. This patent discloses a supplementary hot water heating system for transferring water to a hot water tank. The heating system includes a coil positioned in the flue pipe which is supplied with water from a cold water supply and feeds the heated water to a conventional water tank.
In each of the above devices, the heat exchanger, such as a coil, is positioned directly in the flow path of the exhaust gases. A disadvantage of this arrangement is that the heat exchangers create resistance in the flue pipe and restrict the flow of exhaust gases to the outside. In addition, the coils positioned directly in the flue can cause deposits on the coils, which can be difficult to clean. To overcome this disadvantage, several devices have been proposed that surround an existing flue pipe to recover heat from the exhaust gases. For example, U.S. Pat. No. 5,823,175 to Sweitzer et al. discloses a sleeve surrounding a flue pipe where the sleeve forms a jacket. Water is supplied through the jacket to preheat the water which is then supplied to a conventional hot water heater.
The above-noted devices have been generally successful for their intended purpose of recovering waste heat. However, there is a continuing need in the industry for an improved heat recovery system for extracting waste heat from an exhaust gas.
The present invention is directed to a heat recovery system for recovering waste heat from an exhaust gas flue. In particular, the invention is directed to a heat exchanger connected to a flue pipe for recovering waste heat and preheating water for domestic hot water use.
Accordingly, a primary aspect of the invention is to provide a heat exchanger with an outer water jacket surrounding a flue pipe where the water jacket does not interfere with the flow of exhaust gases through the flue pipe.
Another aspect of the invention is to provide a heat exchanger in direct contact with the outer surface of a flue pipe having an outer water jacket with at least one baffle therein to provide a tortuous path of the water flowing through the jacket.
A further aspect of the invention is to provide a heat exchanger cooperating with a flue pipe for recovering waste heat where the heat exchanger includes an outer water jacket surrounding the flue pipe and where the jacket includes a spiral baffle to produce a spiral path to the water passing through the jacket.
Still another aspect of the invention is to provide a heat recovery system for recovering waste heat from exhaust gases where the system includes a water jacket surrounding a flue pipe and a plurality of holding tanks in direct contact with the outer wall of the jacket and in fluid communication with the jacket.
A further aspect of the invention is to provide a heat recovery system for recovering waste heat from exhaust gases where the system includes an outer water jacket surrounding a flue pipe and a spiral wound pipe surrounding the flue pipe at the upstream end and at the downstream end of the water jacket where the water flows continuously through the spiral wound pipes and the water jacket.
A further aspect of the invention is to provide a heat recovery system including a heat exchanger surrounding a flue pipe where the heat exchanger includes a water jacket surrounding the flue pipe and several water tanks connected in series surrounding the water jacket and connected to the water jacket for supplying water from the tanks to the water jacket.
The various aspects of the invention are basically attained by providing a water heating assembly comprising a furnace for discharging hot exhaust gases and having a flue pipe for discharging the hot exhaust gases. The flue pipe has an axial passage with an inlet end for receiving the hot combustion gases and an outlet end for discharging the hot combustion gases. The flue pipe has an outer surface and an inner surface defining the axial passage. A first baffle member is coupled to the inner surface of the flue pipe and extends inwardly into the axial passage to produce turbulence of the exhaust gases flowing through the axial passage. A substantially cylindrical sleeve is provided which has an upstream end at the upstream end of the flue pipe and a downstream end at the downstream end of the flue pipe. The sleeve is spaced outwardly from the flue pipe to define a water jacket in contact with and surrounding the flue pipe. An inlet pipe is coupled to the downstream end of the sleeve for feeding water into the water jacket. An outlet pipe is coupled to the upstream end of the sleeve for discharging water from the water jacket. A plurality of water tanks is arranged parallel to each other and are connected together in series for feeding water sequentially through each of the water tanks. The water tanks are in heat exchange contact with the sleeve and are arranged to surround the sleeve. At least one of the water tanks is connected to the inlet pipe of the water jacket. A first heat exchange pipe encircles the flue pipe a plurality of turns at the downstream end and is in heat exchange contact with the flue pipe. The first heat exchange pipe has an inlet end connected to a water supply and an outlet end coupled to at least one of the water tanks. A second heat exchange pipe encircles the flue pipe a plurality of turns at the upstream end and is in heat exchange contact with the flue pipe. The second heat exchange pipe has an inlet end coupled to the outlet pipe for receiving water from the water jacket and an outlet end for supplying hot water.
The aspects of the invention are further attained by providing a water heating assembly comprising a flue pipe having an inlet end for receiving hot exhaust gases and an outlet end for discharging the exhaust gases. A substantially cylindrical sleeve is provided which has an upstream end at the upstream end of the flue pipe and a downstream end at the downstream end of the flue pipe. The sleeve is spaced outwardly from the flue pipe to define a water jacket in contact with the flue pipe. An inlet pipe is coupled to the downstream end of the sleeve for feeding water into the water jacket. An outlet pipe is coupled to the upstream end of the sleeve for discharging water from the water jacket. A plurality of water tanks are arranged parallel to each other and are connected together in series for feeding water sequentially through each of the water tanks. The water tanks are in heat exchange contact with the sleeve and are arranged to surround the sleeve. At least one of the water tanks is connected to the inlet pipe. A first heat exchange pipe encircles the flue pipe a plurality of turns at the downstream end and is in heat exchange contact with the flue pipe. The first heat exchange pipe has an inlet end connected to a water supply and an outlet end coupled to at least one of the water tanks. A second heat exchange pipe encircles the flue pipe a plurality of turns at the upstream end and is in heat exchange contact with the flue pipe. The second heat exchange pipe has an inlet end coupled to the outlet pipe for receiving water from the water jacket and an outlet end for supplying hot water.
The aspects of the invention are also attained by providing a heat exchange assembly comprising a flue pipe having an upstream end for receiving hot exhaust gases and a downstream end for discharging the exhaust gases. A sleeve surrounds the flue pipe and has an upstream end and a downstream end. The upstream end is proximate the upstream end of the flue pipe. The sleeve is spaced outwardly from the flue pipe to define a water jacket. The water jacket has a water inlet at the downstream end of the flue pipe and a water outlet at the upstream end of the flue pipe. A plurality of parallel water holding tanks contact an outer surface of the sleeve. Each of the water holding tanks has an inlet at a first end and an outlet at a second end, and are connected together in series. At least one of the water holding tanks has a respective inlet connected to a water source for supplying water sequentially through each of the water holding tanks. At least one of the holding tanks has its respective outlet connected to the inlet of the water jacket at the downstream end of the flue pipe, whereby water flows through the water holding tanks and the water jacket.
These and other aspects of the invention will become apparent from the following detailed description of the invention in conjunction with the annexed drawings which form a part of this original disclosure.